Steam-assisted catalytic–pyrolysis reforming of refinery vacuum residue over Ce- and Rb-promoted Ni catalysts supported on activated carbon for hydrogen-enriched gas and liquid-product upgrading

Vacuum residue (VR) is a highly aromatic, asphaltene-rich refinery stream whose conversion into hydrogen and transport-fuel-range liquids remains challenging. This study examines two-stage steam-assisted pyrolysis–catalytic reforming using Ni catalysts supported on almond-shell-derived activated carbon and promoted with Ce or Rb. Catalysts containing about 15 wt% Ni and 3 wt% promoter were prepared by wet impregnation. Steam reduced solid-residue formation, whereas Ni promoted secondary cracking and reforming. At a final furnace setpoint of 725 °C under the programmed steam-assisted condition, Ni/AC produced 36.8 ± 0.2 wt% gas containing 50.9 vol% H₂, equivalent to approximately 11.0 mmol H₂ g −1 VR. Ce promotion increased the gas yield to 39.8 ± 0.1 wt%, reduced the solid-residue yield to 6.2 ± 0.2 wt%, and gave the highest H₂ concentration and absolute H₂ yield, 57.3 vol% and approximately 15.0 mmol H₂ g −1 VR, respectively. Rb produced intermediate hydrogen yields but shifted liquids more strongly toward lower-carbon-number, naphtha-range compounds. Thus, Ce favoured hydrogen generation, whereas Rb favoured lighter liquid products. Overall, promoter-tuned catalysts enabled simultaneous hydrogen-rich gas production and liquid upgrading.